Ink for ink jet printing and method of using the ink

ABSTRACT

An ink for ink jet printing systems, preferably for continuous jet systems, contains as primary components coloring agents, organic solvents, conductivity mediators, and at least two binding agents, wherein the first binding agent is a bonding agent, and the second binding agent is a fixing agent and an agent for adjusting the viscosity. The ink is used for printing or writing on objects of plastics material, particularly rubber or silicone.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an ink on the basis of solventsfor ink jet printing systems, particularly continuous jet systems. Theinvention also relates to a method of using the ink for printing onrubber or silicone.

[0003] 2. Description of the Related Art

[0004] Inks used in ink jet printing technology for printing on variousrubber materials are known in principle. Such inks are essentiallycomposed of solvents, coloring agents and binding agents. Pigments aswell as dyes are used as coloring agents.

[0005] A disadvantage of such inks is their insufficient abrasionresistance and insufficient bonding to various types of plasticsmaterials, especially on various types of rubber and silicone.

[0006] For evaluating the adherence, frequently the so called adhesivefilm test is used. When this test is performed, a film is placed on anarea imprinted with ink, the film is pressed on and then pulled offagain. In this test, a measure of the adherence of the ink on thesubstrate is the quantity of the ink residues which adhere to theadhesive film and which have been separated from the printed area whenthe film was pulled off.

[0007] It has also been found to be disadvantageous that markingsprinted on such plastics materials, especially rubber and silicone, caneasily be rubbed off with the fingers or wear off quickly during dailyuse, and the imprints, which sometimes contain important information,become illegible or unattractive.

[0008] For example, EP 0 730 014 A1 discloses an ink jet ink forprinting on non-porous surfaces, such as glass, metal or plasticcontainers, wherein the imprints are supposed to have a high rubresistance to alcohol. These inks have the disadvantage that theiradherence to rubber and silicone is insufficient. A large portion of theimprint is separated from the printed surface when the adhesive filmtest is performed.

[0009] U.S. Pat. No. 4,168,254 discloses an ink jet ink for printing oncables encased in polymer, wherein the ink contains a resin for fixingthe coloring agent on a substrate. Such an ink has the disadvantage thatthe abrasion resistance is achieved only by heating to a hightemperature. The supplied heat activates a chemical reaction whichcauses cross-linking of the binding agent.

SUMMARY OF THE INVENTION

[0010] Therefore, it is the primary object of the present invention toprovide an ink on the basis of solvents for ink jet printing,particularly for continuous jet systems, which does not have thedisadvantages described above and which has a good adherence to almostall plastics materials and other smooth components and surfaces.

[0011] An ink for ink jet printing systems, particularly continuous jetsystems, is primarily composed of coloring agents, organic solvents,conductivity mediators and at least one binding agent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In accordance with the present invention, the ink contains aspecial mixture of at least two different binding agents.

[0013] The first binding agent is a bonding agent or also called primer,which preferably is a chemically modified polypropylene, a chemicallymodified low-chlorine polypropylene and/or low-chlorine polypropylene.

[0014] The first binder may also be a chemically modified polyethylene.

[0015] These binders have especially also in combination with the othercomponents a very high affinity to rubber and silicone.

[0016] The second binding agent is preferably selected from acrylicpolymers on the basis of iso-butyl methacrylate, methyl methacrylateand/or ethylacrylate. These binding agents serve primarily for fixingthe coloring agent contained in the ink on the printed substrate, andfor adjusting the viscosity to ensure that the ink operates withoutproblems in the printing device. An optimum viscosity for continuous jetprinting is in the range of 1-10 mPas.

[0017] In the following, the present invention will be described indetail in connection with several ink examples.

EXAMPLE 1 (BASIC EXAMPLE)

[0018] 50 to 85% by weight solvent,

[0019] 0.5 to 18% by weight first binding agent as bonding agent,

[0020] 0.1 to 15% by weight second binding agent as fixing agent,

[0021] 2 to 15% by weight coloring agent,

[0022] 0.2 to 1.5% by weight conductivity mediator,

[0023] 0 to 5% by weight additional additives

EXAMPLE 2 (WHITE INK)

[0024] 71.5% by weight ketone as solvent,

[0025] 6% by weight bonding agent (first binding agent),

[0026] 11% by weight acrylate resin (second binding agent),

[0027] 11% by weight TiO₂ as coloring agent,

[0028] 0.5% by weight conductivity mediator

EXAMPLE 3 (BLACK INK)

[0029] 79.2% by weight ketone as solvent,

[0030] 4% by weight bonding agent (first binding agent),

[0031] 10% by weight acrylate resin (second binding agent),

[0032] 6% by weight solvent black 29 as coloring agent,

[0033] 0.8% by weight conductivity mediator

EXAMPLE 4 (VIOLET INK)

[0034] 79.2% by weight ketone as solvent,

[0035] 4% by weight bonding agent (first binding agent),

[0036] 10% by weight acrylate resin (second binding agent),

[0037] 6% by weight acid violet 66 as coloring agent,

[0038] 0.8% by weight conductivity mediator

[0039] Each of the inks of examples 1-4 contains as an organic solvent aketone, such as acetone and/or ethyl methyl ketone, to which may beadded cyclohexanone, ethylacetate, isopropanol and/or aromatic agents.

[0040] The solvents used should not dissolve the plastics materialswhich are to be imprinted.

[0041] The coloring agents used may be pigments, such as titanium oxideor dyes, such as solvent black 29, a chromium complex, solvent black 28,or acid violet 66, an azochromium complex.

[0042] However, in addition to the coloring agents already mentionedabove, other compatible dyes or color pigments may be used.

[0043] It is irrelevant in this connection whether the dyes are presentin the dry or liquid state. Also, the pigments which are used may bepresent in the pure state or in so called pigment preparations.

[0044] The conductivity mediators contained in the ink may be potassiumthiocyanate, lithium nitrate and/or sodium perchlorate.

[0045] Such an ink is especially suitable for use for printing orwriting on objects of plastics materials, particularly rubber orsilicone substances.

[0046] The invention is not limited by the embodiments described abovewhich are presented as examples only but can be modified in various wayswithin the scope of protection defined by the appended patent claims.

We claim:
 1. An ink for ink jet printing systems, the ink comprisingcoloring agents, organic solvents, conductivity mediators, and first andsecond binding agents which differ from each other, wherein the firstbinding agent is a bonding agent and the second binding agent is afixing agent and means for adjusting the viscosity.
 2. The ink accordingto claim 1, wherein the first binding agent is selected from the groupconsisting of a chemically modified polypropylene, a chemically modifiedlow-chlorine polypropylene and a low-chlorine polypropylene.
 3. The inkaccording to claim 1, wherein the first binding agent is a chemicallymodified polyethylene.
 4. The ink according to claim 1, wherein thesecond binding agent is an acrylic polymer on the basis of iso-butylmethacrylate, methyl methacrylate and/or ethyl acrylate.
 5. The inkaccording to claim 1, wherein the ink comprises 50 to 85% by weightsolvent, 0.5 to 18% by weight first binding agent as bonding agent, 0.1to 15% by weight second binding agent, 2 to 15% by weight coloringagent, 0.2 to 1.5% by weight conductivity mediator, and 0 to 5% byweight other additives.
 6. A method of using an ink for ink jet printingsystems, the method comprising printing or writing an ink composed ofcoloring agents, organic solvents, conductivity mediators, a firstbinding agent as bonding agent, and a second binding agent as a fixingagent and means for adjusting the viscosity, on objects of plasticsmaterial, particularly rubber or silicone substances.